Electrical switch with electrostatic prevention of arc formation



March 21, 1967 H. GREBER 3,310,649

' ELECTRICAL SWITCH WITH ELECTROSTATIC PREVENTION OF ARC FORMATION Filed Oct. 21. 1964 FIGZ INVENTOR United States Patent ELECTRICAL SWITCH WITH ELECTROSTATIC The purpose of this invention is to provide an electrical load breaking device which is able to interrupt large currents without significant wear to its contacts. This device can be used as a switch, disconnector, starter, contactorQor breaker; and can function either in air, or in any other insulating medium, such as gas or oil. This purpose is achieved by means of introducing an in sulating barrier, which separates the movable from stationary contacts, at the moment of current interruption. The mentioned, and further advantages of this device will become apparent from this specification and the accompanying drawing, in which: FIG. 1 is an isometric view of stationary and movable contacts, with an insulating deposit on both, FIG. 2 is an isometric view of a stationary contact provided with an insulating barrier connected to a separate spring, while the movable blade carries, at its bottom, an insulating bar. In FIG. 3 is shown an isometric view of a stationary contact provided with an, attached to it insulating barrier, with the lower part of the blade covered with an insulating bar.

In detailed consideration of the attached drawing it can be seen that the stationary contact 1, shown in FIG- URE 1, is provided, on its top, with an insulating deposit 2, and 3. The movable blade contact 4 has also an insulating deposit 5, on its lower edge. In FIGURE 2 it can be seen that stationary contact 6 is covered with insulating barriers 7 and 8, both fastened to a U-shaped steel spring 9. Blade 10, constituting the movable contact is covered, at its lower edge, with taped, insulating bar 11. Bar 11 is fastened to blade 10, by means of screws 12 and 13, shown in dotted lines. In FIGURE 3 is presented a stationary contact, 14, provided with two wedge-shaped, insulating barriers 15 and 16. These barriers are fastened to the stationary contacts by means of screws, of which two, 17 and 18, are shown. The movable contact 19, which has the form of a blade, carries on its lower part a wedge-shaped insulating bar 20, which is fastened to the blade by meansof the dovetail 21.

The insulating barriers and bars are made of porcelain, ceramics, steatite, mica or asbestos. The deposits referred to in FIGURE 1 are made of enamel, lacquer, glaSS, or of their combinations with the above named, insulating materials. The deposits can also be made by oxidation of the metal of the contacts. The insulatingbarriers and bars are fastened to the contacts, either with screws, or by dovetails. Also plastic, or other cements, as well as sintering can be used for this purpose. For high voltage switches, all surfaces of them, except the ones participating in the transfer of the current from the stationary to the movable contact, have to be covered with insulating materials.

In operation of this switching means, as soon as movable contact loses its metallic connection with the stationary one, the insulating barrier enters the gap between the two contacts. The insulating bar on the lower part of the movable contact prevents the formation of a spark, in the time interval between the loss of metallic connection between the contacts, and when the insulating barrier completely closes the gap formed between them. Since the material of which the insulating barriers and bars can be made, have an about 1000 times greater breakdown voltage than has air, and an about times greater breakdown voltage than has oil, a solid insulating barrier, aided with an insulating baron the movable contact, even if both are comparatively thin, is sufficient to prevent a restroke between the parted contacts. The above holds true for airbreak switches, as well as for circuit breakers and starters operating in oil, and for breakers functioning in insulating gas, such as sulfur-hexafluoride. A modification of the described mode of operation of this device can be achieved by using, for the movable as well as for the stationary contacts, deposits consisting of two layers. The first layer, near the surfaces of the contacts consists of a material of high electrical resistivity, such as graphite with any suitable binder. The first layer is covered with a second layer, which is insulating. The second layer is made of any of the insulating materials mentioned before.

Another modification of the mode of operation of the presented device can be achieved by incorporating electrets into the insulating barriers and bars, or in the deposits, as shown in FIGURE 1. The eleotrets, enclosed in the insulating material, would form a space charge, preventing thus a restroke between the parting contacts.

Still another modification of the described mode of operation of this switching device can be achieved by admixing beta-radioactive substance into the insulating material used for barriers, bars and deposits, as described in the preceding examples. Also beta-radioactive materials would form a space charge preventing any restroke between the separated contacts.

As mentioned, this switching device can be used for any kind of circuit opening and closing operations, be it in airbreak, or disconnect switches, or in starters, contactors Working in oil, or in breakers working in air, gas or oil, and, of course, for all kinds of control switches. Because of the dielectric strength of the solid materials used for insulating barriers, bars and deposits, this switching device is well suitable for high voltage applications. However for very high voltages, the thickness of the insulating barrier would have to be considerable. But even with thick barriers, the speed of separation of the contacts would have to be great, in order .to prevent the formation of a spark. No limitation of the magnitude of the interrupted current exists.

Many modifications and variations of this invention are feasible, without departure from its essence and within the scope of the following claims.

I claim:

1. An electrical switching means, comprising stationary and movable contacts, with said contacts covered, on their sides nearest each other in their disconnected position, with a deposit of insulating material containing electrets, which forms an electrostatic field surrounding them, thus preventing the formation of an are between said stationary and movable contacts.

2. An electrical switching means comprising stationary and movable contacts, with said contacts covered, on their sides nearest each other in their disconnected position, with a deposit of insulating material containing betaradioactive material, which forms a cloud of electrons surrounding said material, thus preventing the formation of an are between said stationary and movable contacts.

References Cited by the Examiner UNITED STATES PATENTS 550,411 11/1895 Harper 200-15] 565,244 8/1896 Tobey et al 200-149 649,554 5/1900 Schwedtmann 200151 751,028 2/1904 Thomson 20015l 1,784,697 12/1930 Martin et a1. 200-151 ROBERT K. SCHAEFER, Primary Examiner. K. A. CLAFFY, H. O. JONES, Assistant Examiners. 

1. AN ELECTRICAL SWITCHING MEANS, COMPRISING STATIONARY AND MOVABLE CONTACTS, WITH SAID CONTACTS COVERED, ON THEIR SIDES NEAREST EACH OTHER IN THEIR DISCONNECTED POSITION, WITH A DEPOSIT OF INSULATING MATERIAL CONTAINING ELECTRETS, WHICH FORMS AN ELECTROSTATIC FIELD SURROUNDING 